1. Field of the Invention
The present invention relates to a keyboard assembly which is formed of key units molded in single pieces from a mold, and a frame in which the key units are mounted.
2. Prior Art
Conventional keyboard assemblies for use in electronic organs and the like include a type in which key units are mounted in a frame forming part of a casing. The key units are each constructed such that a plurality of keys are joined to a common key support via respective connecting portions, the keys, the common key support, and the connecting portions being formed in one piece to simplify the manufacturing process. In a keyboard assembly of this type, however, keys of the key unit are juxtaposed with very small gaps defined between adjacent keys, which necessitates forming a mold for forming the key unit in one piece such that portions or ribs of the mold corresponding to the gaps are very small in thickness. Therefore, the mold has degraded strength and is difficult to fabricate. To cope with this, in the conventional keyboard assembly, instead of making one white key unit per octave, two white key units are made per octave by separately molding them, and then putting the key units together. This leads to a complicated manufacturing process.
In attempt to eliminate these disadvantages, there has been proposed a method of manufacturing a keyboard assembly by Japanese Patent Publication (Kokoku) No. 1-43959, which has a plurality of keys molded in one piece with base ends thereof joined together to serve as a common key support such that gaps between adjacent keys become progressively larger toward front or free ends thereof, and after the molding, the base ends or common key support is forcibly deformed such that the keys extend just parallel with each other.
The proposed method employs two manufacturing manners. According to a first manufacturing manner, an elastic metal sheet which assumes a straight comb-like shape in a free state is used as a material for forming part of the common key support in the completed key unit. The metal sheet with base ends of the keys connected to a comb-shaped side thereof is set into a mold in a state being resiliently deformed in the form of an arc with its comb-shaped side extended, followed by pouring hot resin into the mold. With cooling and curing of the resin, the base ends of the keys become secured to teeth of the extended comb-shaped side of the metal sheet, so that a key unit is formed with the keys radially extending. Then, the metal sheet is released from the resiliently deformed state, whereby the key unit is completed with the keys integrally formed with the comb-shaped side of the metal sheet and extending parallel with each other.
According to a second manufacturing manner, a common connecting portion (base ends) which is curved in a free state and white keys are formed in one piece by molding such that the white keys radially extend from the connecting portion, and after the molding, the connecting portion is forcibly resiliently deformed such that the white keys extend parallel with each other, and then black keys are secured by set screws to predetermined portions of the white keys to form a key unit with white keys and black keys. The key unit is then mounted in a frame. V-shaped or U-shaped grooves are formed in a rear side of the connecting portion at locations between adjacent white keys to facilitate resilient deformation of the connecting portion.
According to the first manufacturing manner, the resiliently deformable common key support has to be separately fabricated in advance, and further, a step of resiliently deforming the common key support with its comb-shaped side extended is required when setting the same into the mold, thus making the manufacturing process complicated and hence still leaving room for further improvement in the simplicity of the manufacturing process.
According to the second manufacturing manner, the key unit is mounted in the frame with the connecting portion resiliently deformed. As a result, a feeling of rubbing of adjacent keys is generated due to variations in size and shape. Moreover, residual stress is present in the connecting portion, which can cause loosening of set screws in the connecting portion after the lapse of a long time after delivery of the product and hence causing a feeling of rubbing of adjacent keys. Thus, the product is disadvantageous in respect of quality and performance.